When the Lord appears before Isaiah in chapter 6 he is scared… pretty scared:
5 “Woe to me!” I cried. “I am ruined!
He knows that no one sees the Lord and lives. He knows he is just a human, but more than that he is sinful and lives amongst a sinful people.
His sin is atoned by the altar in verse 7, as was the place of sacrifice within Israel but later Isaiah will signal a greater atonement to come. A suffering servant will be introduced who will become the new place for atonement.
But for now the nation stares down the barren of judgement, where even the remanent will be laid to waste:
13 And though a tenth remains in the land,
it will again be laid waste.
Judgement will have to come, before salvation can rise from the ashes.
Isaiah’s experience of salvation is a sign God will do a mighty work to his people. He will bring atonement. He will bring cleansing to the sinful through judgement.
Judgment leading to salvation = The Cross.